docs: def combine_expression_columns(df, columns_to_combine, remove_combined=True):
  
      """
      Combine expression columns, calculating the mean for 2 columns
  
  
      :param df: Pandas dataframe
      :param columns_to_combine: A list of tuples containing the column names to combine
      :return:
      """
  
      df = df.copy()
  
      for ca, cb in columns_to_combine:
          df["%s_(x+y)/2_%s" % (ca, cb)] = (df[ca] + df[cb]) / 2
  
      if remove_combined:
          for ca, cb in columns_to_combine:
              df.drop([ca, cb], inplace=True, axis=1)
  
      return df